Feedwater control method and apparatus



Nov. 24, 1942. C B. ARNOLD 2,302,931

FEEDWATER CONTROL METHOD AND APPARATUS Filed 'April e. 1940 "22.SUPER/WAUW@ o 45 OLER DRUM g y 46/ 5 /0 T0 STEAM M10/N v ATTORNPatented Nov. 24, 1942 r OFFICE FEEDWATER CONTROL METHOD AND 'APPARATUSl Charles B. Arnold, Hempstead, N. Y.

1940, serial No. 328,218y

Application April 6,

9 Claims.

This 'invention relates to feedwater control method and apparatus andmore particularly to a boiler feedwater control system which willcompensate for the eiects of varying boiler rating to maintainthedesired water level in the boiler.

-In the operation of steam boilers the water in l,

the boiler vappears to lswell or shrink during changes inthe rate ofsteam output. This apparent or shrinking is due to changes of steambubble'volume in the boiler Water during load changes. In consequence,the Water level rises f momentarily during an increase in load and fallsmomentarily during-a decrease in load. Where the feedwater to the boileris regulated solely upon'changes of waterv level in the boiler, theswelling or shrinking of the water increases or decreases the weight ofwater above the lower tap, which is generally above the bottom of theboiler, and produces the same eiTect on the regulating apparatus asanfactual increaseor de- Avcrease in the quantity Aof 'water in theboiler, thereby causing'unsatisfactor'y regulation.

With straight water levelcontrol, the flow of water to the boiler can bedecreased only by a rise of water level, and increased only by a fall ofWater level. This requires that the water level be maintained higher atlow loads than at high loads, which is an undesirable characteristicwhen the boiler is required to operate under variable load conditions.Assume that the boiler is steaming aty a low rate with a relatively high.I

water level and the load is suddenly increased. Thesudden swell of thewater due to the ncreased steam ebullition, will raise the already highlevel even higher and may, under extreme conditions, cause slugs ofWater to be carried outofv'the` boiler with the steam. On the otherhand, if the boiler load is suddenly decreased the water in the boilerwill shrink to a lower level 4and may, under some conditions, force thelevel dangerously low.

Further, with straight level control, the rise 'and fallo'f water leveldue to swell or shrinkage of boiler water during load changes causeserratic feedwater regulation. Upon an increase of load the feedwatervalve is rst momentarily closed due to the rise of water level, and isnot opened until the water level lowers due to a deciency of Watersupply. Conversely, the fall of water level Which momentarily follows adecrease in load opens the feedwater valve when it should close down.These momentary reverse actions of the regulator during load changesproduce 'a hunting condition wherein either too a considerable `periodof time is required before an equilibrium condition of input and outputis established.jv H i. Y f y The fpre'sent 'invention overcomes theaforementioned `disadvantages` by providinga device whichwill regulatethe ow of water to the boiler in'close'r accord with boiler output atall times. It-'isone of the'obJ'ects of the present invention.to-provide'a feedwater control method and apparatus by which the supplyof water to the boiler vis controlled by factors responsive to loadon'the boilery as Well as to water level so that the water supply isnotdecreased momentarily upon an increase of load nor increased momentarilyupona decrease lof load due to swelling orshrink ingof waterin theboiler. I

' Another object' ofthe invention is to provide a feedwater' controlmethod and apparatus which will enable? ahigher water level 4to bemaintained in the boiler at `high loads than at low loads which is inaccord with rather than contrary to the normal swelling orxshrinkingyof'the boiler water during load changes and `thus permit the waterlevel: to be maintained within 'closer limf its...

Still another'object of the invention is to provide a feedwater controlapparatus which is relativelyv simpleA and inexpensive to'v constructand which is readily adaptable for installation on existing'boilers'I-he above and other objects, advantages and novel 'features of theinvention will be apparent from the:following description of theembodiment shown Vin the accompanyingdrawing,y in which: f

Figure l is adiagrammaticview illustrating a boiler feedwater controlsystem embodying the invention; and

' Figure 2 is an enlarged section of the heat eX- change unit of Figure1.-

In Figure 1 the boiler drum is indicated generally at IU and is providedwith a ysight glass I2 for indicating the level of Water in the boiler.A Vsecond sight glass I4 is connected to the boiler atI above the Waterlevel therein 'and atV I8 below the water level in the boiler.'Asuperheater indicated at 20 is provided in connection with the boilerand `discharges intoy a header 22 from which steam may be withdrawn to'any ldesired point of use. Water is supplied to the vboiler througha'pipe 24 by a feedwater pump 26, a valve 28 being provided to controlthe rate of water supply.

According to the present invention an extermuch Aortoo ,little water isfed to the boiler and 55 nal circulating system Vis provided shownv asbeing formed of a plurality of conduit sections 30, 32, 34 and 36. Theconduit 30 is connected to the water connection I8 and a valve 38 isprovided to regulate the flow therethrough. If desired, a drain valve 40may be connected to the lower part of the circulating system to drainwater therefrom.

The sight glass I4 is connected at its lower end to the conduit 30 andat its upper end to a conduit 42 leading from the connection I6. Ifdesired, a conduit 44 in parallel with the sight glass may be provided.

Circulation through the secondary circuit is established by leading apipe 46 from the superheated steam header 22 through a vertical leg 36of the circulating system. A valve 48 is provided in the pipe 46 andtemperature gauges 50 may be connected to the pipe above and below theconduit section 36. At its lower end the pipe 46 may lead to the steammain from the boiler.

The valve 28 is controlled by a water'level responsive regulator whichmay be of the type shown in the patent to Smoot, No. 1,904,554 includinga wobble pot 52 including interconnected mercury chambers mounted on aweigh-beam 54 and having its opposite sides connected to the conduits 30and 42. The weigh-beam 54 controls a power unit 56 which moves an arm 58vertically to open and close the Valve 28 through a connection 60. Thepower unit may be a uid motor as shown in Smoot Patent No. 1,904,554controlled through the weigh beam by a pilot valve to move the outer endof the arm 58 vertically thereby to control the valve 28. In operation,the pressure kon the left side of the wobble pot normally exceeds thaton the right side tending to tilt the weigh beam counterclockwise tomove the arm 58 downwardly thereby to close the valve 28 to compensatefor an increase in water level in the boiler.

With a device of this character the regulator will control the valve 28so as to maintain a constant differential across the wobble pot therebyresulting in a higher water level in the boiler at high ratings than atlow ratings. In order to compensate for this effect a characteristicspring is provided at 62 connected under tension to the arm 58 and theweigh beam 54. The spring normally urges the weigh beam to turn in a.clockwise direction partially to balance the tilting force of the wobblepot and as the arm 58 is moved up or down by the power unit, the springwill exert a varying tension on the weigh beam providing a variablecharacteristic dependent upon the position of the arm 58 and the valve.Thus in different positions of the valve a different differential on thewobble pot will rebalance the weigh beam so that the water level in theboiler will be maintained more nearly constant at all times.

The conduit section 36 is illustrated in somewhat more detail in Figure2 as including an elongated tubular casing having an inlet connection 64at its lower end for connection with the pipe 34 and an outletconnection 66 at its upper end for connection with the pipe 38. Theopposite ends of the tube are closed by plugs 68 welded or otherwisepermanently secured in place,

and each of which is formed with a relatively f small central opening10. A coiled pipe 12 extends longitudinally through the casing 36 withits ends projecting through the openings 1I) and terminating inconnectors 14 for connection to the pipe 46. One method of securing theparts illustrated, is to connect the ends of the coil 12 and theconnectors 14 to plates 16, which may be bolted to the end closures 68as shown. The coil 12 is preferably so formed that it may be threadedthrough one of the openings 10 somewhat in the manner of a corkscrew sothat it may be removed or replaced without disturbing the end closures68.

In operation of the system the valve 48 should be adjusted so that thetemperature of steam leaving the pipe 46 at the lower end of the casing36 is slightly, for example about 5 F., above the temperature of waterin the boiler at approximately maximum load. With the boiler operatingat about its maximum capacity the valve 38 should then be adjusted untilthe level in the sight glass I4 is below that in the sight glass I2, anamount equal to the desired compensation; for example, 6". Thecharacteristic spring 62 on the regulator should then be adjusted toapply force on the weigh-beam which will substantially balance out theamount of compensation.

After these adjustments have been made the system is ready for operationand will operate as follows. Superheated steam from the header 22 willflow through the coil 12 in the casing 36 and will heat water andgenerate steam therein to establish a thermal circulation through theconduits 38, 32 and 34. Heating of the water in the casing 315 and theconsequent steaming will reduce the density of the water column in thecasing 36 causing some of the water therein to enter the boiler throughthe connectionV I8 and this will cause a pressure in the pipe 30 lessthan that which would normally exist therein due to the circulating flowthrough the restriction of the valve 38. This, in eiect, will lower thewater level in the sight glass I4 so that it is less than the actualWater level in the boiler as indicated by the sight glass I2'. by anamount proportional to the reduction of pressure caused by circulationin the circulating system. Since the regulator is connected, in effect,across the sight glass I4 it regulates the supply of water to the-boilerin accordance with this compensated level.

If the load on the boiler should be increased, an increased quantity ofsteam will flow through the conduit 46 to increase circulation in theexternal conduit system. This will effect a. greater reduction ofpressure in the conduit 30 and Will compensate for the eiect of swellingof the water in the boiler so that the feedwater valve 28 will not beclosed. Conversely, if the load should be decreased the flow of steamthrough conduit 46 will decrease so that less compensation will beprovided, thereby to neutralize the effect of shrinking .of the water.

The system has the further effect of controlling the valve 28 to providea higher water level at high loads than at low loads. This may be duepartially to the compensating action of the external circulating systemand partially to the effect of the characteristic spring 26 on theregulator.

While one embodiment of the invention has been shown and described indetail it will be understood that this is illustrative only and is notintended as a definition of the scope of the invention, reference beinghad for this purpose to the appended claims.

What is claimed is:

l. The method of controlling the supply of water to a steam boiler whichcomprises creating a differential pressure proportional to the head inplace, as

of water in the boiler, creating an external circulation of fluid in acircuit closed except for communication with the boiler proportional toa function of the flow of steam from the boiler, reducing saiddifferential by an amount proportional to a function of the rate of saidcirculation, and controlling the supply of water to the boiler inaccordance with the reduced differential.

2. The method of controlling the supply of water to a steam boiler whichcomprises creating a differential pressure proportional to the head ofwater in the boiler, heating water external to the boiler by flow ofsteam from the boiler, causing said water to circulate in response tothe rate of heating, reducing the differential by an amount proportionalto a function of the rate of water circulation, and controlling thesupply of water to the boiler by the reduced differential.

3. Feedwater control apparatus for steam boilers comprising connectionsto the boiler above and below the normal water level therein, meansforming a complete water circuit external to the boiler, a steamconnection from the boiler through a vertical part of said circuit toheat the water and generate steam therein to set up a thermalcirculation in said circuit, a connection from said circuit to one ofsaid boiler connections to modify the water level effect, means tosupply water to the boiler, and control means connected to the boilerconnections to vary said water supply in accordance with changes in themodified water level.

4. Feedwater control apparatus for steam boilers comprising connectionsto the boiler above and below the normal water level therein, means tosupply water to the boiler, control means for the water supply connectedto the boiler connections, means forming a complete water circuitexternal to the boiler, a superheater associated with the boiler tosuperheat steam therefrom, means to circulate steam from the superheaterthrough a vertical part of said circuit to heat the water and generatesteam therein, and a connection from said circuit to one of the boilerconnections between the boiler and the control means to modify the waterlevel effect in pro'- portion to a function of the rate of circulationin the circuit.

5. Feedwater control apparatus for steam boilers comprising connectionsto the boiler above and below the normal water level therein, meansforming a complete water circuit external to the boiler, a superheaterassociated with the boiler to superheat steam therefrom, means tocirculate steam from the superheater through a vertical paril of saidcircuit to heat the water and generate steam therein, a connection fromsaid circuit to one of the boiler connections to modify the Water leveleffect in proportion to a function of the rate of circulation in thecircuit, means to supply water to the boiler, control means for thesupply means, a regulator controlling said control means, andconnections from the regulator to the boiler connections beyond theconnection from said circuit to one of the boiler connections, theregulator including a characteristic spring to oppose the tendency ofthe regulator to provide a higher water level at high boiler ratingsthan at low boiler ratings.

6. Feedwater control apparatus for steam boilers comprising connectionsto the boiler above and below the normal water level therein, meansforming a complete water circuit external to the to one of the boilerconnections to modify the water level effect in accordance with the rateboiler, a connection from said circuit to the boiler below the waterlevel therein, means in a vertical part in said circuit to circulatesteam from the boiler therethrough to cause a thermal circulation in thecircuit, a connection from the circuit to one of the boiler connectionsto modify the water level effect in accordance with the rate ofcirculation in the circuit, means to supply water to the boiler, andcontrol means for the supply means connected to the boiler connectionsbeyond the connection from said Acircuit to one of the boilerconnections and responsive to the pressures therein.

7. Feedwater control apparatus for steam boilers comprising connectionsto the boiler above and below the normal water level therein, meansforming a complete water circuit external to the boiler, a connectionfrom said circuit to the boiler below the water level therein, asuperheater con nected to the boiler, means in a vertical part of saidcircuit to circulate steam from the superheater therethrough to cause athermal circulation in the circuit, a connection from the circuit orrcirculation in the circuit, means to supply water to the boiler, andcontrol means for the supply means connected to the boiler connectionsbeyond the connection from said circuit to one of the boiler connectionsand responsive to the pressures therein.

8. Feedwater control apparatus for steam boilers comprising connectionsto the boiler above and below the normal water level therein, a seriesof conduits forming a complete circulating system external to theboiler, one of said conduits being formed by an enlarged casingextending vertically and formed with inlet and outlet connections at itslower and upper ends, a coil extending vertically through the casing,steam connections from the boiler to said coil, a connection from thecircuit to one of the boiler connections to modify the water leveleffect in accordance with the rate of circulation in the circuit, meansto supply water to the boiler, and control means for the supply meansconnected to the boiler connections beyond the connection from saidcircuit to one of the boiler connections and responsive to the pressurestherein.

9. Feedwater control apparatus for steam boilers comprising connectionsto the boiler above and below the normal water level therein, a seriesof conduits forming a complete circulating system external to theboiler, one of said conduits being formed by an enlarged casingextending vertically and formed with inlet and outlet connections at itslower and upper ends, the ends of said casing having relatively smallopenings therein, a coil extending vertically through the casing withits ends projecting 'through said openings, said coil being so formedthat it may be threaded through one of said openings without removingthe end of the casing, steam connections from the boiler to said coil, aconnection from the circuit to one of the boiler connections to modifythe water level effect in accordance with the rate of circulation in thecircuit, means to supply water tothe boiler, and control means for thesupply means connected to the boiler connections beyond the ,connectionsfrom said circuit to one of the boiler connections and responsive to thepressures therein.

CHARLES B. ARNOLD.

CERTIFICATE vOF CORRECTION Patent No.` 2,502,951. November 2li, 1914.2.

' CHARLES B. ARNOLD.

It is hereby certifiedthat error appears in the printed specification ofthe above nwnberedv patent requiring eorreotion as follows: Page lyfirst,column-, line before "or" insert "swellingpage 5, second column, line5, claim 6, for in said read of said; f and line TO, Claim 9, for "theconnections read --the oonneotion; and that the said Letters Patentshould be read with this correction therein that the same may conf l fomto. the record of the case in the Patent Offige. l

signed and sealed this 13th day of January, A. D. 19u?.

Y Henry Van Arsdalie, (Seal) Acting Commissioner of Patents

